None of the references described or referred to herein are admitted to be prior art to the claimed invention.
Diagnostic assays are widely used in clinical diagnosis and health science research to detect or quantify the presence or amount of biological antigens, cell or genetic abnormalities, disease states, and disease-associated pathogens or genetic mutations in an organism or biological sample. Where a diagnostic assay permits quantification, practitioners may be better able to calculate the extent of infection or disease and to determine the state of a disease over time. Diagnostic assays are frequently focused on the detection of chemicals, proteins or polysaccharides antigens, antibodies, nucleic acids, amino acids, biopolymers, cells, or tissue of interest. A variety of assays may be employed to detect these diagnostic indicators.
Nucleic acid-based assays, in particular, generally include multiple steps leading to the detection or quantification of one or more target nucleic acid sequences in a sample. The targeted nucleic acid sequences are often specific to an identifiable group of proteins, cells, tissues, organisms, or viruses, where the group is defined by at least one shared sequence of nucleic acid that is common to members of the group and is specific to that group in the sample being assayed. A variety of nucleic acid-based detection methods are fully described by Kohne, U.S. Pat. No. 4,851,330, and Hogan, U.S. Pat. No. 5,541,308.
Detection of a targeted nucleic acid sequence frequently requires the use of a probe comprising a nucleic acid molecule having a nucleotide base sequence that is substantially complementary to at least a portion of the targeted sequence or its complement. Under selective assay conditions, the probe will hybridize to the targeted sequence or its complement in a manner permitting a practitioner to detect the presence of the targeted sequence in a sample. Techniques of effective probe preparation are known in the art. In general, however, effective probes are designed to prevent non-specific hybridization with itself or any nucleic acid molecule that will interfere with detecting the presence of the targeted sequence. Probes may include, for example, a label capable of detection, where the label is, for example, a radiolabel, a fluorophore or fluorescent dye, biotin, an enzyme, a chemiluminescent compound, or another type of detectable signal known in the art.
To detect different nucleic acids of interest in a single assay, different probes configured to hybridize to different nucleic acids, each of which may provide detectably different signals can be used. For example, different probes configured to hybridize to different targets can be formulated with fluorophores that fluoresce at a predetermined wavelength when exposed to excitation light of a prescribed excitation wavelength. Assays for detecting different target nucleic acids can be performed in parallel by alternately exposing the sample material to different excitation wavelengths and detecting the level of fluorescence at the wavelength of interest corresponding to the probe for each target nucleic acid during the real-time monitoring process. Parallel processing can be performed using different signal detecting devices constructed and arranged to periodically measure signal emissions during the amplification process, and with different signal detecting devices being configured to generate excitation signals of different wavelengths and to measure emission signals of different wavelengths.
Because the probe hybridizes to the targeted sequence or its complement in a manner permitting detection of a signal indicating the presence of the targeted sequence in a sample, the strength of the signal is proportional to the amount of target sequence or its complement that is present. Accordingly, by periodically measuring, during an amplification process, a signal indicative of the presence of amplicon, the growth of amplicon overtime can be detected. Based on the data collected during this “real-time” monitoring of the amplification process, the amount of the target nucleic acid that was originally in the sample can be ascertained. Exemplary systems and methods for real time detection and for processing real time data to ascertain nucleic acid levels are described, for example, in Lair, et al., U.S. Pat. No. 7,932,081, “Signal measuring system for conducting real-time amplification assays.”.
Challenges may arise, however, when measuring emission signals during an amplification process or other process. The target sequence or its complement, or other emission signal source, may be contained in a receptacle that is held within an incubator or other processing module that is fully or partially enclosed and for which access by a signal detector to the receptacle or other source for measuring the emission signal may not be practical. Moreover, for space utilization efficiencies and/or other efficiencies (such as thermal efficiencies), the receptacles or other emission signal sources may positioned in a spatial arrangement for which it is not efficient or practical to place a signal detector in operative position to measure the emission signals. For example, a plurality of receptacles or emission signal sources may be arranged in a rectangular arrangement whereby the receptacles are closely spaced in multiple rows of two or more receptacles each. In such a spatial arrangement, it may not be practical or efficient to provide a signal detector for each receptacle position or to move a signal detector with respect to the receptacle positions to sequentially measure signal emissions from each of the receptacles.